package util;

import java.util.Iterator;
import java.util.NoSuchElementException;

/**
 * <p>A hash map that uses primitive ints for the key rather than objects.</p>
 *
 * <p>Note that this class is for internal optimization purposes only, and may
 * not be supported in future releases of Apache Commons Lang.  Utilities of
 * this sort may be included in future releases of Apache Commons Collections.</p>
 *
 * @author Apache Software Foundation
 * @author Justin Couch
 * @author Alex Chaffee (alex@apache.org)
 * @since 2.0
 * @version $Revision: 1.2 $
 * @see java.util.HashMap
 */
public class IntHashMap<V> implements Iterable<V> {

    /**
     * The hash table data.
     */
    private transient Entry<V> table[];

    /**
     * The total number of entries in the hash table.
     */
    private transient int count;

    /**
     * The table is rehashed when its size exceeds this threshold.  (The
     * value of this field is (int)(capacity * loadFactor).)
     *
     * @serial
     */
    private int threshold;

    /**
     * The load factor for the hashtable.
     *
     * @serial
     */
    private final float loadFactor;
    
    /**
     * Last iterator object.
     */
    private transient ValueIterator lastIterator;
    
    /**
     * Last iteration thread.
     */
    private transient Thread lastIterationThread;

    /**
     * <p>Innerclass that acts as a datastructure to create a new entry in the
     * table.</p>
     */
    private static class Entry<V> {
        final int hash;
        final int key; // TODO not read; seems to be always same as hash
        V value;
        Entry<V> next;

        /**
         * <p>Create a new entry with the given values.</p>
         *
         * @param hash The code used to hash the object with
         * @param key The key used to enter this in the table
         * @param value The value for this key
         * @param next A reference to the next entry in the table
         */
        protected Entry(int hash, int key, V value, Entry<V> next) {
            this.hash = hash;
            this.key = key;
            this.value = value;
            this.next = next;
        }
    }

    /**
     * <p>Constructs a new, empty hashtable with a default capacity and load
     * factor, which is <code>20</code> and <code>0.75</code> respectively.</p>
     */
    public IntHashMap() {
        this(20, 0.75f);
    }

    /**
     * <p>Constructs a new, empty hashtable with the specified initial capacity
     * and default load factor, which is <code>0.75</code>.</p>
     *
     * @param  initialCapacity the initial capacity of the hashtable.
     * @throws IllegalArgumentException if the initial capacity is less
     *   than zero.
     */
    public IntHashMap(int initialCapacity) {
        this(initialCapacity, 0.75f);
    }

    /**
     * <p>Constructs a new, empty hashtable with the specified initial
     * capacity and the specified load factor.</p>
     *
     * @param initialCapacity the initial capacity of the hashtable.
     * @param loadFactor the load factor of the hashtable.
     * @throws IllegalArgumentException  if the initial capacity is less
     *             than zero, or if the load factor is nonpositive.
     */
    public IntHashMap(int initialCapacity, float loadFactor) {
        super();
        if (initialCapacity < 0) {
            throw new IllegalArgumentException("Illegal Capacity: " + initialCapacity);
        }
        if (loadFactor <= 0) {
            throw new IllegalArgumentException("Illegal Load: " + loadFactor);
        }
        if (initialCapacity == 0) {
            initialCapacity = 1;
        }

        this.loadFactor = loadFactor;
        table = new Entry[initialCapacity];
        threshold = (int) (initialCapacity * loadFactor);
    }

    /**
     * <p>Returns the number of keys in this hashtable.</p>
     *
     * @return  the number of keys in this hashtable.
     */
    public int size() {
        return count;
    }

    /**
     * <p>Tests if this hashtable maps no keys to values.</p>
     *
     * @return  <code>true</code> if this hashtable maps no keys to values;
     *          <code>false</code> otherwise.
     */
    public boolean isEmpty() {
        return count == 0;
    }

    /**
     * <p>Tests if some key maps into the specified value in this hashtable.
     * This operation is more expensive than the <code>containsKey</code>
     * method.</p>
     *
     * <p>Note that this method is identical in functionality to containsValue,
     * (which is part of the Map interface in the collections framework).</p>
     *
     * @param      value   a value to search for.
     * @return     <code>true</code> if and only if some key maps to the
     *             <code>value</code> argument in this hashtable as
     *             determined by the <tt>equals</tt> method;
     *             <code>false</code> otherwise.
     * @throws  NullPointerException  if the value is <code>null</code>.
     * @see        #containsKey(int)
     * @see        #containsValue(Object)
     * @see        java.util.Map
     */
    public boolean contains(V value) {
        if (value == null) {
            throw new NullPointerException();
        }

        Entry tab[] = table;
        for (int i = tab.length; i-- > 0;) {
            for (Entry e = tab[i]; e != null; e = e.next) {
                if (e.value.equals(value)) {
                    return true;
                }
            }
        }
        return false;
    }

    /**
     * <p>Returns <code>true</code> if this HashMap maps one or more keys
     * to this value.</p>
     *
     * <p>Note that this method is identical in functionality to contains
     * (which predates the Map interface).</p>
     *
     * @param value value whose presence in this HashMap is to be tested.
     * @return boolean <code>true</code> if the value is contained
     * @see    java.util.Map
     * @since JDK1.2
     */
    public boolean containsValue(V value) {
        return contains(value);
    }

    /**
     * <p>Tests if the specified object is a key in this hashtable.</p>
     *
     * @param  key  possible key.
     * @return <code>true</code> if and only if the specified object is a
     *    key in this hashtable, as determined by the <tt>equals</tt>
     *    method; <code>false</code> otherwise.
     * @see #contains(Object)
     */
    public boolean containsKey(int key) {
        Entry tab[] = table;
        int hash = key;
        int index = (hash & 0x7FFFFFFF) % tab.length;
        for (Entry e = tab[index]; e != null; e = e.next) {
            if (e.hash == hash) {
                return true;
            }
        }
        return false;
    }

    /**
     * <p>Returns the value to which the specified key is mapped in this map.</p>
     *
     * @param   key   a key in the hashtable.
     * @return  the value to which the key is mapped in this hashtable;
     *          <code>null</code> if the key is not mapped to any value in
     *          this hashtable.
     * @see     #put(int, Object)
     */
    public V get(int key) {
        Entry<V> tab[] = table;
        int hash = key;
        int index = (hash & 0x7FFFFFFF) % tab.length;
        for (Entry<V> e = tab[index]; e != null; e = e.next) {
            if (e.hash == hash) {
                return e.value;
            }
        }
        return null;
    }

    /**
     * <p>Increases the capacity of and internally reorganizes this
     * hashtable, in order to accommodate and access its entries more
     * efficiently.</p>
     *
     * <p>This method is called automatically when the number of keys
     * in the hashtable exceeds this hashtable's capacity and load
     * factor.</p>
     */
    protected void rehash() {
        int oldCapacity = table.length;
        Entry oldMap[] = table;

        int newCapacity = oldCapacity * 2 + 1;
        Entry newMap[] = new Entry[newCapacity];

        threshold = (int) (newCapacity * loadFactor);
        table = newMap;

        for (int i = oldCapacity; i-- > 0;) {
            for (Entry old = oldMap[i]; old != null;) {
                Entry e = old;
                old = old.next;

                int index = (e.hash & 0x7FFFFFFF) % newCapacity;
                e.next = newMap[index];
                newMap[index] = e;
            }
        }
    }

    /**
     * <p>Maps the specified <code>key</code> to the specified
     * <code>value</code> in this hashtable. The key cannot be
     * <code>null</code>. </p>
     *
     * <p>The value can be retrieved by calling the <code>get</code> method
     * with a key that is equal to the original key.</p>
     *
     * @param key     the hashtable key.
     * @param value   the value.
     * @return the previous value of the specified key in this hashtable,
     *         or <code>null</code> if it did not have one.
     * @throws  NullPointerException  if the key is <code>null</code>.
     * @see     #get(int)
     */
    public V put(int key, V value) {
        // Makes sure the key is not already in the hashtable.
        Entry<V> tab[] = table;
        int hash = key;
        int index = (hash & 0x7FFFFFFF) % tab.length;
        for (Entry<V> e = tab[index]; e != null; e = e.next) {
            if (e.hash == hash) {
                V old = e.value;
                e.value = value;
                return old;
            }
        }

        if (count >= threshold) {
            // Rehash the table if the threshold is exceeded
            rehash();

            tab = table;
            index = (hash & 0x7FFFFFFF) % tab.length;
        }

        // Creates the new entry.
        Entry<V> e = new Entry<V>(hash, key, value, tab[index]);
        tab[index] = e;
        count++;
        return null;
    }

    /**
     * <p>Removes the key (and its corresponding value) from this
     * hashtable.</p>
     *
     * <p>This method does nothing if the key is not present in the
     * hashtable.</p>
     *
     * @param   key   the key that needs to be removed.
     * @return  the value to which the key had been mapped in this hashtable,
     *          or <code>null</code> if the key did not have a mapping.
     */
    public V remove(int key) {
        Entry<V> tab[] = table;
        int hash = key;
        int index = (hash & 0x7FFFFFFF) % tab.length;
        for (Entry<V> e = tab[index], prev = null; e != null; prev = e, e = e.next) {
            if (e.hash == hash) {
                if (prev != null) {
                    prev.next = e.next;
                } else {
                    tab[index] = e.next;
                }
                count--;
                V oldValue = e.value;
                e.value = null;
                return oldValue;
            }
        }
        return null;
    }

    /**
     * Interface emulator.
     * @return
     */
    public IntHashMap<V> values() {
    	return this;
    }
    
    /**
     * <p>Clears this hashtable so that it contains no keys.</p>
     */
    public synchronized void clear() {
        Entry<V> tab[] = table;
        for (int index = tab.length; --index >= 0;) {
            tab[index] = null;
        }
        count = 0;
    }
    
    /**
     * Implements Iterable interface.
     */
    public synchronized Iterator<V> iterator() {
    	if (lastIterator != null && lastIterationThread == Thread.currentThread()) {
    		lastIterator.currentSlot = -1;
    		lastIterator.currentEntry = null;
    	} else {
    		lastIterator = new ValueIterator();
    		lastIterationThread = Thread.currentThread();
    	}
    	return lastIterator;
    }
    
    /**
     * Implements Iterable interface.
     */
    public Iterator<V> iterator2() {
    	return new ValueIterator();
    }
    
    /**
     * The class used to iterate values in map.
     * @author lighthu
     */
    private class ValueIterator implements Iterator<V> {
	    /*
	     * Current iteration pointer.
	     */
	    private int currentSlot = -1;
	    /*
	     * Current iteration entry.
	     */
	    private Entry<V> currentEntry;
	    /*
	     * Next entry.
	     */
	    private V nextEntry;
	    
	    /*
	     * Get next entry.
	     * @see java.util.Iterator#next()
	     */
	    public V getNextEntry() {
	    	V ret = null;
	    	
	    	// If there are more elements in current slot, return next element.
	    	if (currentEntry != null && currentEntry.next != null) {
	    		ret = currentEntry.next.value;
	    		currentEntry = currentEntry.next;
	    		return ret;
	    	}
	    	
	    	// Seek for next non-empty slot
	    	currentEntry = null;
	    	while (currentSlot < table.length - 1 && currentEntry == null) {
	    		currentSlot++;
	    		currentEntry = table[currentSlot];
	    	}
	    	if (currentEntry == null) {
	    		return null;
	    	} else {
	    		return currentEntry.value;
	    	}
	    }

	    /**
	     * Returns <tt>true</tt> if the iteration has more elements. (In other
	     * words, returns <tt>true</tt> if <tt>next</tt> would return an element
	     * rather than throwing an exception.)
	     *
	     * @return <tt>true</tt> if the iterator has more elements.
	     */
	    public boolean hasNext() {
	    	if (nextEntry == null) {
	    		nextEntry = getNextEntry();
	    	}
	    	return nextEntry != null;
	    }
	
	    /**
	     * Returns the next element in the iteration.
	     *
	     * @return the next element in the iteration.
	     * @exception NoSuchElementException iteration has no more elements.
	     */
	    public V next() {
	    	if (nextEntry != null) {
	    		V ret = nextEntry;
	    		nextEntry = null;
	    		return ret;
	    	} else {
	    		return getNextEntry();
	    	}
	    }
	
	    /**
	     * 
	     * Removes from the underlying collection the last element returned by the
	     * iterator (optional operation).  This method can be called only once per
	     * call to <tt>next</tt>.  The behavior of an iterator is unspecified if
	     * the underlying collection is modified while the iteration is in
	     * progress in any way other than by calling this method.
	     *
	     * @exception UnsupportedOperationException if the <tt>remove</tt>
	     *		  operation is not supported by this Iterator.
	     
	     * @exception IllegalStateException if the <tt>next</tt> method has not
	     *		  yet been called, or the <tt>remove</tt> method has already
	     *		  been called after the last call to the <tt>next</tt>
	     *		  method.
	     */
	    public void remove() {
	    	if (currentEntry == null) {
	    		return;
	    	}
	    	for (Entry<V> e = table[currentSlot], prev = null; e != null; prev = e, e = e.next) {
	            if (e == currentEntry) {
	                if (prev != null) {
	                    prev.next = e.next;
	                    currentEntry = prev;
	                } else {
	                    table[currentSlot] = e.next;
	                    currentEntry = null;
	                    currentSlot--;
	                }
	                count--;
	                return;
	            }
	        }
	    }
    }
}
